Things you can do:
1. Do you have children in your game? (Klamath is the earliest point in the game you can check this - they'll run around in the first area). If so, it's US.
2. Check the readme file. Either in the heading or some way down it should say which version it belongs to.
3. If the letters "ELV" are on your CD, you're screwed, but chances of that should be small.